1. Field of the Invention
The present invention relates to a semiconductor structure and a method for manufacturing the same. More particular, the present invention relates to a low-temperature polysilicon thin film transistor structure for a liquid crystal display with a high aperture ratio and a method for manufacturing the same.
2. Descriptions of the Related Art
Low luminance has been a key issue for thin film transistor liquid crystal displays (TFT-LCDs). As a result, efforts to improve the aperture ratio of pixels have been made over recent years. The aperture ratio refers to the ratio of the light-transmissive area to the total area in a TFT-LCD. A high aperture ratio allows more light to be projected outwards sufficiently and efficiently with less light loss in the TFT liquid crystal panel. Hence, the higher the aperture ratio is, the more light will be transmitted. Accordingly, many manufacturers are developing new manufacturing processes to improve the aperture ratio of TFT-LCDs in expectation of providing both high luminance and low power consumption.
A conventional pixel structure with a high aperture ratio in an LCD is depicted in FIG. 1. In this pixel structure, the data line 11 is comprised of a first metal layer 111 and a second metal layer 112. In the semiconductor manufacturing process, different metal layers are formed at different levels. To interconnect the different metal layers, contact holes are opened in the dielectric interlayer between these metal layers at positions where these metal layers are overlapped with each other, so that the metal layers may be electrically interconnected through the contact holes. Commonly, the contact holes between metal layers are generally termed as “vias” for distinguishing purposes. In FIG. 1, the data line 11 has contact holes 113, 114 to electrically interconnect the first metal layer 111 and the second metal layer 112 and to have the data line 11 cross over another line 115 formed in the first metal layer 111 for vertical electrical conduction.
To ensure that the electrical connection characteristics between the metal layers (e.g., impedance) are not disturbed by the contact holes, the dimensions of the contact holes must comply with specific design rules. In general, the opening dimension of the contact hole must be wide enough to avoid excessively high connection impedance. Meanwhile, there is also a risk of wire breakage because the metal layers are electrically connected via a contact hole.
As described above and illustrated in the pixel structure of FIG. 1, the two contact holes must inevitably be opened in the data line. Because the contact holes 113, 114 must be formed into a specific size to maintain appropriate connection impedance, the aperture ratio of the pixel structure will inevitably be reduced by forming the contact holes 113, 114. Meanwhile, because the two contact holes 113, 114 are formed in the data line 11, the risk of wire breakage is increased for the data line 11. In other words, when the first and the second metal layers 111, 112 are interconnected via the contact holes, wire breakage may occur in the data line 11 due to yield control variation of the manufacturing process, making it impossible to maintain electrical connection.
Accordingly, efforts still have to be made in the art to provide a semiconductor structure that delivers a high aperture ratio in an LCD and to also ensure satisfactory electrical characteristics of the pixel structures in the LCD.